The arithmetic sequence $(a_i)$ is defined by the formula: $a_i = 5 + 6(i - 1)$ What is $a_{13}$, the thirteenth term in the sequence?
Solution: From the given formula, we can see that the first term of the sequence is $5$ and the common difference is $6$ To find $a_{13}$ , we can simply substitute $i = 13$ into the given formula. Therefore, the thirteenth term is equal to $a_{13} = 5 + 6 (13 - 1) = 77$.